Combined Immunodeficiency Patients Research Articles

Flow cytometry analysis of adenosine deaminase (ADA) expression: a simple and reliable tool for the assessment of ADA-deficient patients before and after gene therapy.

Clinical gene therapy trials for adenosine deaminase (ADA) deficiency have shown limited success of corrective gene transfer into autologous T lymphocytes and CD34(+) cells. In these trials, the levels of gene transduction and expression in hematopoietic cells have been assessed by DNA- or RNA-based assays and measurement of ADA enzyme activity. Although informative, these methods are rarely applied to clonal analysis. The results of these assays therefore provide best estimates of transduction efficiency and gene expression in bulk populations based on the assumption that gene transfer and expression are uniformly distributed among transduced cells. As a useful additional tool for evaluation of ADA gene expression, we have developed a flow cytometry (fluorescence-activated cell sorting, FACS) assay capable of estimating the levels of intracellular ADA on a single-cell basis. We validated this technique with T cell lines and peripheral blood mononuclear cells (PBMCs) from ADA-deficient patients that showed severely reduced levels of ADA expression (ADA-dull) by FACS and Western blot analyses. After retrovirus-mediated ADA gene transfer, these cells showed clearly distinguishable populations exhibiting ADA expression (ADA-bright), thus allowing estimation of transduction efficiency. By mixing ADA-deficient and normal cells and using enzymatic amplification, we determined that our staining procedure could detect as little as 5% ADA-bright cells. This technique, therefore, will be useful to quickly assess the expression of ADA in hematopoietic cells of severe combined immunodeficient patients and represents an important tool for the follow-up of patients treated in clinical gene transfer protocols.

Molecular basis for paradoxical carriers of adenosine deaminase (ADA) deficiency that show extremely low levels of ADA activity in peripheral blood cells without immunodeficiency.

Adenosine deaminase (ADA) deficiency causes an autosomal recessive form of severe combined immunodeficiency and also less severe phenotypes, depending to a large degree on genotype. In general, ADA activity in cells of carriers is approximately half-normal. Unexpectedly, healthy first-degree relatives of two unrelated ADA-deficient severe combined immunodeficient patients (mother and brother in family I; mother in family II) had only 1-2% of normal ADA activity in PBMC, lower than has previously been found in PBMC of healthy individuals with so-called "partial ADA deficiency." The level of deoxyadenosine nucleotides in erythrocytes of these paradoxical carriers was slightly elevated, but much lower than levels found in immunodeficient patients with ADA deficiency. ADA activity in EBV-lymphoblastoid cell lines (LCL) and T cell lines established from these carriers was 10-20% of normal. Each of these carriers possessed two mutated ADA alleles. Expression of cloned mutant ADA cDNAs in an ADA-deletion strain of Escherichia coli indicated that the novel mutations G239S and M310T were responsible for the residual ADA activity. ADA activity in EBV-LCL extracts of the paradoxical carriers was much more labile than ADA from normal EBV-LCL. Immunoblotting suggested that this lability was due to denaturation rather than to degradation of the mutant protein. These results further define the threshold level of ADA activity necessary for sustaining immune function.

Techniques for studying development of human natural killer cells and T cells.

It is now commonly accepted that natural killer (NK) cells are closely related to T cells. Some severe combined immunodeficiency (SCID) patients have been described lacking T and NK cells, but having normal numbers of B and myeloid cells, suggesting a common origin of T and NK cells (). Furthermore, T and NK cells share a number of phenotypic and functional characteristics, not present in B cells (reviewed in [,]). In additional, both in humans () and mice () cells have been found with T and NK cell, but no B cell, progenitor activities

Development of improved adenosine deaminase retroviral vectors.

A series of adenosine deaminase (ADA) retroviral vectors were designed and constructed with the goal of improved performance over the PA317/LASN vector currently used in clinical trials. First, the bacterial selectable-marker neomycin phosphotransferase (neo) gene was removed to create a "simplified" vector. Second, the Moloney murine leukemia virus long terminal repeat (LTR) promoter used for ADA expression was replaced with either the myeloproliferative sarcoma virus (MPSV) or SL3-3 LTR. Supernatant from each ADA vector was used to transduce ADA-deficient (ADA-) B- and T-cell lines as well as primary peripheral blood mononuclear cells (PBMC) from an ADA- severe combined immunodeficiency patient. Total ADA enzyme activity and ADA activity per integrant in the transduced cells demonstrated that the MPSV LTR splicing vector design provided the highest level of ADA expression per cell. This ADA(MPSV) vector was then tested in packaging cell lines containing either the gibbon ape leukemia virus envelope (PG13 cells), the murine amphotropic envelope (FLYA13 cells), or the feline endogenous virus RD114 envelope (FLYRD18 cells). The results indicate that FLYRD18/ADA(MPSV), a simplified ADA retroviral vector with the MPSV LTR, provides a 17-fold-higher level of ADA expression in human lymphohematopoietic cells than the PA317/LASN vector currently in use.

Engrafted maternal T cells in human severe combined immunodeficiency: Evidence for a T H2 phenotype and a potential role of apoptosis on the restriction of T-cell receptor variable β repertoire

1. Street MD, Donovan GR, Baldo BA, Sutherland S. Immediate allergic reactions to Myrmecia ant stings; immunochemical analysis of Myrmecia venoms. Clin Exp Allergy 1994;24:590-7. 2. Donovan GR, Baldo BA, Sutherland S. Molecular cloning and characterisation of a major allergen (Myr p 1) from the venom of the Australian jumper ant. Biochim Biophys Acta 1993;1171:272-80. 3. Weiner JM, Baldo BA, Donovan GR, Sutherland SK. Allergy to jumper ant (Myrmecia pilosula) stings in south-eastern Australia [abstract]. Ann Allergy Asthma Immunol 1995;74:60. 4. Stuckey M, Cobain T, Sears M, Cheney J, Dawkins RL. Bee venom hypersensitivity in Busselton [letter]. Lancet 1982;2:41.

X-SCID B cell responses to interleukin-4 and interleukin-13 are mediated by a receptor complex that includes the interleukin-4 receptor alpha chain (p140) but not the gamma c chain.

This study investigates the effect of interleukin (IL)-4 mutant proteins and a monoclonal antibody to the IL-4 receptor alpha chain on IL-4 and IL-13 response by B cells from X-linked severe combined immunodeficiency (X-SCID) patients in which the common gamma chain (gamma c chain) gene mutations have been fully characterized and no gamma c chain expression was detected. In this gamma c chain gene knockout model, it was confirmed that the gamma c chain is essential for B cell responses to IL-2 but not for IL-4 or IL-13. Dose-response curves for X-SCID and normal B cell responses to IL-4 were indistinguishable, showing that the loss of the gamma c chain did not diminish the sensitivity of B cells to IL-4. The mutant protein IL-4(Y124D) and an antibody to the IL-4R alpha chain both inhibited responses of X-SCID B cells to IL-4 and IL-13, showing that X-SCID B cell responses to these cytokines are mediated by a receptor complex that includes the IL-4R alpha chain but not the gamma c chain. Another mutant protein, IL-4(R88D), which has greatly reduced affinity for IL-4R alpha, was found to inhibit responses by normal B cells to IL-4 but not to IL-13. IL-4(R88D), did not, however, inhibit X-SCID B cell responses to IL-4. This result is consistent with IL-4(R88D) inhibition of responses mediated by receptor complexes that include the gamma c chain. We propose that X-SCID B cells responses to IL-4 are mediated by an IL-13 receptor complex comprised of the IL-4R alpha chain associated with the recently cloned IL-13R binding protein. This model has major implications for understanding normal B cell responses to IL-4.

Two novel missense and frameshift mutations in exons 5 and 6 of the purine nucleoside phosphorylase (PNP) gene in a severe combined immunodeficiency (SCID) patient.

Four percent of human severe combined immunodeficiency cases are caused by a deficiency of the enzyme purine nucleoside phosphorylase (PNP). In this study we investigated the molecular basis for this rare autosomal recessive disease. Sequence analyses led to the identification of two new mutations in the PNP gene: an A to G transition in exon 5, which leads to the substitution of tyrosine 192 by a cysteine residue, and a 1-bp deletion in exon 6, which causes premature translation termination of the PNP protein. Both PNP mutations affect predicted major structural motifs of the protein and result in post-translation instability of the enzyme.

Signal Transduction Pathway of Interleukin-4 and Interleukin-13 in Human B Cells Derived from X-linked Severe Combined Immunodeficiency Patients

Interleukin-4 (IL-4) and IL-13 are functionally similar cytokines. The functional IL-4 receptor (IL-4R) consists of the IL-4R alpha chain (IL-4R alpha) and the IL-2R gamma chain (gamma c), which is shared by the IL-2, IL-7, IL-9, and IL-15 receptors. The functional IL-13R is thought to involve the IL-4R alpha but not gamma c. In this study, we have analyzed activation of members of the Janus tyrosine kinase (Jak) family and signal transducers and activators of transcription (STAT) 6 induced by IL-4 and IL-13 in Epstein-Barr virus-transformed B cells derived from two patients of X-linked severe combined immunodeficiency, who have mutations of the gamma c gene in the extracellular and intracellular domains. In these B cells, IL-4 failed to induce tyrosine phosphorylation of Jak3 and activation of STAT6, or activation of these molecules was significantly decreased compared with Epstein-Barr virus-transformed normal B cells. In contrast, IL-13 activated STAT6 in these cells as well as normal B cells. However, Jak3 was not activated by IL-13, even in normal B cells. These results clearly indicated that gamma c is essential for activation of Jak3 and STAT6 in the signal transduction pathway of IL-4 in human B cells and that IL-13 does not utilize gamma c but activates STAT6 through an alternative pathway, which is not impaired in B cells of X-linked severe combined immunodeficiency patients.

Characterization of B-Cell Lines Established From Two X-Linked Severe Combined Immunodeficiency Patients: Interleukin-15 Binds to the B Cells But Is Not Internalized Efficiently

X-linked severe combined immunodeficiency (XSCID) is characterized by absent or profoundly reduced numbers of T cells and normal numbers of B cells in the circulation. Affected patients have mutations of the interleukin-2 (IL-2) receptor gamma chain gene. Using Epstein-Barr virus-transformed B-lymphoblastoid cell lines (B-LCLs) established from two unrelated XSCID patients, we could show that neither expressed the IL-2 receptor gamma chain on the cell surface. A novel cytokine IL-15, which has biologic activities similar to those of IL-2, could bind to the XSCID B-LCLs in the absence of the gamma chain, although both the beta and gamma chains of the human IL-2 receptor were previously shown to be required for IL-15 binding by transfected COS cells. Furthermore, a significant reduction and delay of IL-15 internalization by B lymphoblasts from XSCID patients was observed when compared with that of normal control B-LCLs. These results show the existence of a novel IL-15-specific receptor component that contributes to IL-15 binding but is insufficient for IL-15 internalization in the absence of the IL-2 receptor gamma chain.

Engrafted Maternal T Cells in a Severe Combined Immunodeficiency Patient Express T-Cell Receptor Variable Beta Segments Characterized by a Restricted V-D-J Junctional Diversity

To better understand the peculiar functional behavior of engrafted maternal T cells in a severe combined immunodeficiency (SCID) patient, we characterized, at the molecular level, the T-cell repertoire of a SCID child with a high number of engrafted, mature, activated lymphocytes. We found that, although these transplacentally acquired T cells express a random set of T-cell receptor variable beta (TCRBV) segments, the TCRBV transcripts are characterized by an extremely restricted V-D-J junctional diversity. Only a few cDNA clones were dominant among the TCRBV4+, TCRBV6+, and TCRBV20+ populations in engrafted cells, whereas the same TCRBV chains expressed by the mother's lymphocytes had the expected junctional hetero-geneity. Highly diverse and polyclonal junctions were also expressed by maternal cells activated in mixed lymphocyte reaction by Epstein-Barr virus (EBV)-transformed B lymphocytes from the patient, indicating that the strong clonal selection that characterizes the engrafted cells repertoire is probably not due to allorecognition. Furthermore, we report that the repertoire of the transplacentally acquired lymphocytes is dynamic over time and is characterized by waves of expression and contraction of selected clones, expressing different TCRBV segments. These results help to explain some of the abnormal functional behaviors of engrafted maternal cells and raise new questions regarding the mechanisms responsible for the restricted clonal diversity.

Endocytosis of the β chain of interleukin‐2 receptor requires neither interleukin‐2 nor the γ chain

Interleukin-2 (IL-2) and IL-2 receptors (IL-2R) critically regulate the magnitude and duration of T cell expansion required in an immune response. Modulation occurs at the level of receptor number and affinity. IL-2R is a multisubunit receptor which contains at least three chains, IL-2R alpha (p55), IL-2R beta (p70) and IL-2R gamma (p64). Some components of high-affinity receptors (alpha beta gamma) are continuously internalized in the absence as well as in the presence of IL-2. From studies on other receptors, it is known that endocytosis of ligand-receptor complexes is due to an intrinsic property of the receptor. However, the specific chains responsible for endocytosis of high-affinity IL-2 receptors have not been fully elucidated. IL-2R gamma has been reported to be necessary for IL-2 internalization, based on the fact that fibroblasts transfected with IL-2R alpha and -beta do not internalize IL-2. However, IL-2 dissociates too rapidly from IL-2R alpha beta receptors to allow for its internalization. From the reported results on IL-2 internalization in transfected fibroblasts, it cannot be concluded as to the respective roles of IL-2R beta and/or IL-2R gamma in endocytosis. As modulation of receptor number is important for biological activity, we have attempted to define the chains responsible for receptor internalization. In this work, we have studied the endocytic properties of IL-2R beta. We demonstrate that IL-2R beta is constitutively endocytosed in a B cell line, derived from a X-linked severe combined immunodeficiency patient, which lacks expression of IL-2R gamma. IL-2R beta was also constitutively internalized in T and natural killer cell lines independently of IL-2R gamma. These results suggest that IL-2R beta is endowed with endocytic capacity and carries internalization signals.

Retroviral vectors containing chimeric promoter/enhancer elements exhibit cell-type-specific gene expression.

Retroviral vectors were constructed in which the U3 promoter/enhancer of Moloney murine leukemia (Mo-MLV) was replaced by the corresponding region from five related murine retroviruses--AKR murine leukemia virus (AKV), Harvey murine sarcoma virus (HaMSV), myeloproliferative sarcoma virus (MPSV), SL3-3, and the NZB-xenotropic virus (Xeno). In these vectors the chimeric long terminal repeat (chLTR) drives the expression of the chloramphenicol acetyl transferase (CAT) reporter gene that is followed by an internal SV40 virus early region promoter linked to the neomycin phosphotransferase II (NEO) gene. As an initial measure of the relative promoter/enhancer strength of the chLTR vectors, the murine NIH-3T3 cell line and the human JURKAT cell lines were transfected and assayed for CAT reporter activity. Relative to the MoMLV vector, the HaMSV construct was the most active in NIH-3T3 cells whereas the SL3-3 vector displayed the greatest activity in JURKAT cells. Retroviral vector producer cell populations and cell clones were established for each chLTR vector, and all were capable of yielding high vector titers (> 10(5) G418R cfu/ml on NIH-3T3). Supernatant from these cells was used to transduce both mouse and human cell lines and primary cells. In NIH-3T3 cells and two murine fibrosarcoma cell lines, the HaMSV chLTR vector was slightly more active than the MoMLV chLTR vector. In the human HepG2 and HeLa cell lines, the MPSV chLTR vector was the most active. Data from the human JURKAT T-cell line and a T cell line derived from an ADA-deficient severe combined immunodeficiency (SCID) patient demonstrate that the SL3-3 chLTR is the most active in these lymphoid cell lines. The greatest difference in the comparison of the different chLTR vectors was observed in primary human umbilical vein endothelial cells, where the MoMLV vector produced up to 100 times more CAT activity than the SL3-3 vector. These data suggest that the use of specific promoter/enhancer elements may lead to higher levels of gene expression following retroviral-mediated gene transfer into specific cell types and these observations may be useful in the design of human gene therapy experiments.

Preferential utilization of the immature JH segment and absence of somatic mutation in the CDR3 junction of the Ig H chain gene in three X-linked severe combined immunodeficiency patients.

Human severe combined immunodeficiency (SCID) includes an X-linked SCID (XSCID) characterized by a complete absence of mature T cells, hypogammaglobulinemia and a normal or elevated number of B cells. XSCID results from mutation in the IL-2 receptor (IL-2R) gamma chain gene, which is thought to be involved in not only IL-2R but also IL-4R and IL-7R mediated signals. To investigate the VDJ recombination and Ig repertoire development in the absence of the IL-2R gamma chain, we intended to study the CDR3 junction in peripheral blood B cells of three XSCID patients. A total of 101 different CDR3 junctions were cloned following polymerase chain reaction amplification of polyclonal peripheral blood lymphocyte DNA. Sequence analysis of CDR3 junctions revealed that the primary antibody repertoire of the Ig H chain gene was assembled in a normal fashion. Among the JH segments, overexpression of JH3 segments was significant in XSCID patients compared with age-matched controls. D segment usage in XSCID was very similar to that in age-matched controls. All of the XSCID JH regions except for two clones were equal to germline JH genes, showing little or no evidence of somatic mutation. The results indicate that the immature JH segment is preferentially utilized and somatic mutation is absent in the CDR3 junction of the Ig H chain gene of XSCID patients.

Three in vivo promoter phenotypes in MHC class II deficient combined immunodeficiency

Major histocompatibility complex (MHC) class II deficient combined immunodeficiency (CID), also referred to as type II bare lymphocyte syndrome (BLS), is a genetic disease which impairs immune responses by abrogating the expression of the MHC class II genes (LisowskaGrospierre et al. 1985). The defect in gene expression is at the transcriptional level and affects all the class II genes coordinately (DePreval et al. 1988). Studies of CID patient families demonstrated that the disease locus segregates independently from the MHC locus (DePreval et al. 1985), which suggested that the defect was not in the MHC genes themselves. This was confirmed by fusing EpsteinBarr virus (EBV)-transformed B-lymphocyte cell lines from CID patients to healthy B-lymphocyte cell lines, which resulted in reexpression of the class II genes (Yang et al. 1988; Hume and Lee 1989; Benichou and Strominger 1991). Thus, the CID defect is thought to reside in a trans-acting regulatory factor(s). Fusion experiments between the various CID cell lines have defined four different genetic complementation groups (Benichou and Strominger 1991). The regulatory factors defective in these cell lines have not yet been identified. However, evidence from DNase I hypersensitivity studies suggested that the chromatin structure of class II promoters is altered in certain CID cell lines (G6nczy et al. 1989). To better characterize the nature of the regulatory defect in class II deficient CID, we have examined the occupancy of class II promoters in various CID cell lines in vivo by genomic footprinting. Using a small number of cell lines and the HLA-DRA gene, we previously demonstrated two different in vivo promoter phenotypes (Kara and Glimcher 1991). Here, we extend this study to a complete panel of CID-derived and experimentally-derived class II-negative cell lines for three class II genes, HLA-DRA, -DRB, and -DQB, and describe a third in vivo phenotype.

Promoter accessibility within the environment of the MHC is affected in class II-deficient combined immunodeficiency.

Class II-deficient combined immunodeficiency (CID) is a hereditary disease resulting in abrogation of transcription of the class II genes of the major histocompatibility complex, due to a defect in a trans-acting regulatory factor. Cell lines from certain CID patients lack factor binding at multiple sites in class II promoters in vivo. A mutation in one of the promoter binding proteins could explain this 'bare' phenotype only if these factors bind cooperatively or in a temporal hierarchy. Alternatively, the mutation could affect the configuration of the promoter within the MHC locus. Here, we provide evidence that the factor(s) defective in class II-deficient CID controls the accessibility of class II promoters within the environment of the MHC. The in vivo occupancy of wild type and mutated class II promoter constructs was examined in stable transfectants of normal and CID-derived cell lines. The CID promoter phenotype could not be reproduced in a normal cell line by eliminating binding at any one promoter element, suggesting that these factors bind independently, both spatially and temporally. In contrast, promoter occupancy was partially restored in two CID lines at a randomly integrated wild type promoter, implying that the promoter is inaccessible to factors in its native environment, but accessible when moved to another location in the genome.

Immunoglobulin kappa light chain germ-line transcripts in human precursor B lymphocytes.

B lymphoblastoid cell lines (BLCL), established from bone marrow and peripheral blood mononuclear cells from two severe combined immunodeficiency (SCID) patients, manifested a complete absence of genomic rearrangements of the immunoglobulin (Ig) heavy (H) and light (L) chain loci. The BLCL contained germ-line transcripts of the Ig kappa region locus of approximately 1.2 kilobase (kb). By cDNA cloning and sequence analysis the transcripts were shown to consist of a C kappa segment, a J kappa 1 gene segment, 160 base pairs (bp) of J kappa 1 5' intervening sequence, containing the heptamer/nonamer recombination recognition sequences and at the 5' end a 523-bp segment designated human kappa zero, The first 206 bp of this 5' segment were homologous to the reported murine kappa zero region. Genomic restriction mapping and DNA sequence analysis demonstrated that the human kappa zero segment is located approximately 4 kb upstream of J kappa 1. The kappa zero segment contains a putative promoter region with an OCT2 binding site, and has a splice donor site to accomplish splicing to an acceptor site 160 bp upstream of J kappa 1. Expression of the kappa zero gene segment was found in BLCL derived from normal fetal bone marrow, in which both Ig kappa loci were in the germ-line configuration. These findings indicate that the described transcripts are not only present in SCID, but also in normal developing pre-B lymphocytes. The expression of germ-line Ig kappa L chain transcripts may be associated with the locus becoming accessible to gene rearrangement.

A combined immunodeficiency with oligoclonal CD8+, V beta 3-expressing, cytotoxic T lymphocytes in the peripheral blood.

The diagnosis severe combined immunodeficiency was made in a male infant at the age of 18 wk. Known causes of severe combined immunodeficiency were excluded. The activity of total 5'-nucleotidase (E.C. 3.1.3.5) in the PBMC was found to be strongly decreased. Analysis of the peripheral blood revealed a lymphocytosis, mainly of CD8+ T cells. These lymphocytes expressed high levels of CD29, CD38, CD45RA, and MHC class II molecules but no CD25, CD26, CD27, or CD28 Ag. The cells proliferated poorly to all T cell stimulants tested and no helper activity for IgM secretion could be induced. In contrast to the poor proliferative responses, high levels of TCR-induced cytolytic activity, without lymphokine-activated killer-cell outgrowth, were induced by CD3 mAb. Analysis of TCR-beta gene rearrangements indicated that two clonal populations constituted the majority of the E-rosette+ peripheral blood fraction. Moreover, the vast majority of the CD8+ cells were found to react with a mAb to V beta 3. Polymerase chain reaction on cDNA from peripheral blood cells with primers that amplify TCR V beta elements showed, in agreement with the fluorescence data, an overrepresentation of V beta 3 but absence of usage of approximately 50% of the other V beta elements. Thus, in a severe combined immunodeficiency patient, CD8+ T cells with limited T cell receptor usage and restricted effector functions were found. The observed alterations in the 5'-nucleotidase levels may be secondary to the outgrowth of this population.

Severe combined immunodeficiency (SCID) in man: B cell-negative (B-) SCID patients exhibit an irregular recombination pattern at the JH locus.

Human severe combined immunodeficiency (SCID) patients were analyzed by a polymerase chain reaction assay for their recombination capability at the DHQ52-JH region of the immunoglobulin heavy chain locus. Five patients with B cells (B+ SCID) exhibited a recombination pattern also observed in healthy persons. In contrast, six patients lacking B cells (B- SCID) showed a grossly altered rearrangement pattern characterized by the (partial) absence of regular DHQ52-JH recombinations and the presence of abnormal rearrangements. These events were caused by deletions surpassing the boundaries of immunoglobulin coding elements and thus resemble the pattern of deletional recombinations previously described in SCID mice.

Self-nonself discrimination and repertoire selection of human T cells differentiated in an HLA-semiallogeneic environment following bone marrow transplantation for severe combined immunodeficiency

We have analyzed allorecognition, HLA restriction and T cell receptor (TcR) diversity in an HLA-heterozygous (HLA-DRw6,7) severe combined immunodeficiency (SCID) patient whose T cell system had been repopulated by HLA-homozygous (HLA-DRw6) paternal T cells following T cell-depleted bone marrow transplantation (BMT). Donor origin of T cells and host origin of antigen-presenting cells (APC) in peripheral blood and BM is shown by HLA typing of separated cell populations and two-color immunofluorescence using an anti-HLA monoclonal antibody (mAb). Peripheral blood lymphocytes (PBL) from the chimeric patient proliferate normally against PHA, anti-TcR/CD3 mAb, pooled allogeneic PBL, and also against the recall antigen (Ag) tetanus toxoid and purified protein derivative of tuberculin (PPD) following immunization, suggesting recognition by donor (DRw6) T cells of Ag presented by host (DRw6,7) APC. PPD-specific cytotoxic T lymphocytes generated in vitro from patient PBL post-BMT display specific cytotoxicity against targets expressing DRw6 and DR7, but not against DR-mismatched targets, suggesting that HLA restriction of Ag recognition may occur through determinants expressed by the host and not by the donor. Donor T cells differentiated in the HLA-semiallogeneic host show specific proliferative and cytotoxic responses against HLA-mismatched stimulators, but not against stimulators taken from the host, expressing the host-specific HLA-haplotype, or expressing the host-specific HLA-DR7 antigens. Compared to T cells directly taken from the donor, differentiation of donor T cells in the host is associated with a significant decrease of T cells expressing TcR V beta 5 and V alpha 2 determinants, while no differences in the abundance of of TcR V beta 6, V beta 8 and V beta 12 subsets were noticed. We conclude that allorecognition, major histocompatibility complex (MHC) restriction and TcR diversity generation of human T cells can be modulated through differentiation in an MHC-different environment, as had been previously shown to be the case in murine model systems.

Limited T cell receptor diversity of transplacentally acquired maternal T cells in severe combined immunodeficiency.

Circulating maternal T lymphocytes were noted in the peripheral blood of six patients with severe combined immunodeficiency. Phenotypical analyses revealed the presence of both CD4 and CD8 subsets in some but not all cases. The maternal T cells could be stimulated by anti-TCR/CD3 mAb +/- rIL-2, but were virtually silent in the MLR and against the recall Ag purified protein derivative of tuberculin and tetanus toxoid, even in immunized patients engrafted with T cells from a responding mother. Using a panel of mAb against TCR V region gene encoded epitopes including V beta 5, V beta 6, V beta 8, V beta 12, and V alpha 2, we show that maternal T cells displayed a profoundly reduced TCR diversity, characterized by a lack of one or even several TCR V subsets in all six cases and a dramatic (5- to 25-fold) expansion of other TCR V subsets in three cases. In one patient analyzed, limited TCR diversity was also seen in T cells cultured from bone marrow and skin; restimulation experiments of these cells against cells expressing host MHC Ag were unsuccessful, as were attempts to exclusively allocate anti-host proliferative responses of maternal control T cells to the TCR V subsets that had undergone expansion in vivo. We conclude that a severely reduced TCR diversity is a common feature of maternal T cells engrafted in severe combined immunodeficiency patients. These novel findings provide a structural basis to understand the failure of these cells to protect the host from infections and may also help to understand their relative inefficiency to induce lethal, multi-organ, graft vs host disease. Moreover, as an experiment of nature, the reported phenomenon clearly illustrates the functional consequences in vivo of an insufficient TCR diversity.